The present invention relates to intravascular devices and, in particular, it concerns semi-retrievable intravascular devices and corresponding methods. The invention also relates to retrieval systems for retrieving intravascular devices, and filter structures for use in intravascular devices.
Co-pending, co-assigned patent applications: U.S. patent application Ser. No. 09/613,760; PCT Patent Application No. IL00/00553; Israel Patent Application No. 143007; and PCT Patent Application No. IL01/00636, describe various filter configurations which include stabilizing elements (helical and/or ring-like elements) which support an inner filter wire. Since the stabilizing elements have rings which are in contact with the vessel wall, if these devices are used for extended periods, the wires of the stabilizing elements become permanently attached to the vessel wall as endothelium grows over them. Subsequent removal of the device then risks causing significant damage to the vessel.
It would therefore be useful to provide devices and corresponding methods which would facilitate extended use of intravascular devices and then subsequently allow removal of at least the part of the device which causes most obstruction to flow through the vessel while avoiding significant damage to the vessel itself.
Turning now to systems for retrieving previously deployed intravascular devices, the predominant retrieval system is based upon a snare mechanism in which a loop is placed wound part of the device and tightened. This mechanism inherently tends to twist the captured device sideways, thereby rendering it difficult to draw the device into a retrieval catheter unless the catheter is greatly oversized. A further problem with the snare mechanism is the difficulty in positioning the loop around part of the device. This typically requires real time imaging techniques, and even then, can be a difficult and time consuming procedure.
There is therefore a need for a retrieval system which tends to align the captured part of an intravascular device so that it can be drawn into a catheter of dimensions only slightly larger than the diameter of the captured part of the device. It would also be highly advantageous to provide a retrieval system which would allow convenient, or even “blind” retrieval, of an intravascular device without complicated manipulation.
Turning finally to intravascular filter structures, a number of options for implementing intravascular filter structures are described in the above-referenced PCT application. For relatively coarse filtering, such as for large emboli in the inferior vena cava (“IVC”), the structures described therein are highly effective. Where finer filtering is required, for example for distal protection during procedures in the carotid artery, the length of wire required to reliably achieve the required filtering effect increases sharply and is non-optimal.
There is therefore a need for intravascular filter structures, both for tethered use and as part of un-tethered devices, which would achieve finer filtering for a given length of wire: